Over the past decade, more stringent laws and regulations have been imposed on companies' discharge of various industrial waste by-products into the waters, lakes and streams. Companies' document pollutant levels in their area to verify that they are complying with these requirements.
The pollutant level in municipal and industrial storm water discharge is a useful parameter in determining a plurality of different pollutant levels. First of all, this can determine the pollutant level in the air, as some of the pollutant level in the air will become dissolved in the rainwater that falls. In addition, there is a certain amount of silt which will also be collected. This silt will be somewhat representative of the pollutant level in and running off from the soil. Oil, grease, and leach ate from stored or spilled chemicals or raw materials can also be found in storm water discharge.
Accordingly, the EPA has issued rules that require that samples be collected from the discharge resulting from a storm event that is greater than 0.1 inches in magnitude and that occurs at least 72 hours from the. previously measurable (greater than 0.1 inch rainfall) storm event. The EPA requires a grab sample shall be taken during the first thirty minutes of the discharge. If the collection of a grab sample during the first thirty minutes is impracticable, a grab sample can be taken during the first hour of the discharge, but then discharge must submit with the monitoring report a description of why a grab sample during the first thirty minutes was impracticable.
In order to comply with these regulations, a grab sampling device is needed that is inexpensive, reliable and is able to be calibrated to take a sample only when a certain level of discharge is present.
There have been many devices proposed to comply with the regulation. A runoff water trap is disclosed in U.S. Pat. No. 4,958,528 to Garrison. It uses a float valve to control when a sample is taken.
U.S. Pat. No. 1,742,400 to Larsson defines a structure which uses a float to open and close a valve. U.S. Pat. No. 2,388,548 to Jurs uses a complicated sequence of weights, pulleys and arms in order to open and close a valve.